System for energizing a cathode ray tube



06%.26, 1937. VON ARDENNE 2,096,987

SYSTEM FOR ENERGIZING A CATHPDE RAY TUBE Filed NOV. 15, 1933 Jnvenfor:

UNITED STATES PATENT OFFICE SYSTEM FOR ENERGIZING A OATHODE RAY TUBE Manfred von Ardenne, Berlin, Germany Application November 13, 1933, Serial No. 697,739 In Germany November 15, 1932 1 Claim.

The invention relates to the particular embodiment of mains apparatus for delaying the initiation of the anode potential in Braun tubes. The use of indirectly heated cathodes in tube apparatus, in Braun tubes, acts detrimentally on the life thereof, owing to the long time required for heating the cathode, if the full anode potential becomes eiTective before the cathode has attained a sufficiently high temperature. Now when using normal mains apparatus the anode potential acquires its full voltage almost instantaneously, whereas the temperature of the cathode, and together therewith the emission, increases only very slowly, and frequently does not attain a sufficiently high value until after an elapse of several minutes. In the interval before the complete emission takes place there is produced a particularly strong cathode fall, which leads to a vigorous bombardment of ions and to a greatly shortened life and a deformation of the cathode, similar to the manner in which, as well known, under-heated cathodes are subject to premature wear or damage in tube apparatus. If the heating period amounts, for example, to 1 minute for an indirectly heated cathode, the dangerous state with the bombardment of ions commences, as experiments have shown after approximately 10 seconds. Said cathode fall is particularly dangerous because of the relatively small surface of the highly emissive material.

According to the invention, these disadvantages are to be overcome by the fact that special measures are taken to prevent the full anode potential from becoming effective at a premature stage, and that the anode potential only attains its full effective value when the cathode has reached a suificiently high temperature and accordingly an adequate emission, which is sufficient to prevent excessive cathode fall in the case of full anode potential, so that a detrimental bombardment of ions is unable to occur.

According to the invention it is possible to accomplish delay in the charging of the condensers f the mains portion, for example by means of series-connected highly ohmic resistances. By the inclusion of highly ohmic resistances in the charging circuit of the rectifier tube the inner resistance of the D. C. generator is diminished, and it is accomplished in reliable fashion that the maximum anode potential is reached automatically only after expiration of the heating period. By the dimensioning of the resistance between the rectifier tube and the condenser, i. e., by dimensioning the time constant of the mains portion, it is possible to perform adaptation to practically any desired cathode. It may also be accomplished that the anode potential in each case does not reach its effective state until the complete emissive temperature of the cathode has been attained both in the case of relatively short as well as long periods of heating of the cathode.

Fig. 1 shows a circuit arrangement of one form of the invention with a short time constant.

Fig. 2 shows a circuit arrangement of another form of the invention with a long time constant.

The invention will now be described more fully with the assistance of certain forms of embodiment. Fig. 1 shows an arrangement as hitherto usual with a mains transformer I, the secondary winding of which feeds the filament 2 of a Braun tube through the medium of a regulating resistance 3, further the cathode 4 of the rectifier tube 5, and finally the Winding 6, which supplies the anode potential. The Wehnelt cylinder 1 of the Braun tube is connected with the anode 8 of the rectifier tube 5. Between the cathode 2 and the Wehnelt cylinder 1 of the Braun tube there is situated a resistance 9, which is bridged by a condenser it. The anode potential is taken from the condenser H and fed to the anode l2 of the Braun tube.

Fig. 2 shows a form of embodiment according to the invention with special dimensioning of the mains portion. The arrangement in itself is the same as in Fig. 1, but according to the invention there is provided in addition to the condenser II a resistance I l and a further condenser l3. If, for example, the condenser H is se- 16Ct6d=lpF', the condenser I3=0.25 F, and the resistance l4=5 megohms, there results in connection with the condenser H a charging period of approximately 10 seconds with a time constant of 4.5 seconds, whereas in the case of Fig. 1 the charging period is approximately sec.

The possible form of embodiment referred to may undergo numerous modifications within the meaning of the invention. It is essential that in each case measures are taken to ensure that the anode potential does not reach its full value until after the elapse of a certain time which is necessary to raise the indirectly heated cathode to a sufficiently high temperature.

I claim:

In a television arrangement the combination of a Braun tube containing an indirectly heated cathode, a control electrode and an anode, power supply apparatus for energizing the cathode of said tube from a source of alternating current, rectifying means for supplying anode potential 55 to said tube from said'sou ce O a t t dura, filter network including parallel connected conmeans f delaying e pplic n f n densers and a series connected resistance, the mal operating potential to the anode until said condensers and resistance being dimensioned to indirectly heated cathode has reached a temexhibit a time constant for anode potential supply perature at which detrimental ion'bombardment delay.

thereupon will not occur; said means comprising MANERED VON ARDENNE. 

